This paper reports on a preliminary investigation into the elaboration, by the additive process known as laser cladding, of composite coatings with a matrix of stainless steel 316L reinforced with varying ... [more ▼]

This paper reports on a preliminary investigation into the elaboration, by the additive process known as laser cladding, of composite coatings with a matrix of stainless steel 316L reinforced with varying contents of tungsten (WC) or silicon carbides (SiC) particles. Laser cladding is characterised by ultra-fast solidification and cooling rates, thus giving rise to ultra-fine out-of-equilibrium microstructures and potentially enhanced mechanical properties. Both types of composite coatings – i.e. with SiC or WC ‒ are compared in terms of their microstructures and hardness. Special attention is given to the dissolution of the carbides particles and to interfacial reactions taking place between the particles and the metallic matrix. [less ▲]

Three examples involving size effects are presented witj implications concerning the formability: small Ni-20wt.%Cr resistive bridges, magnetic micro-sensors performed with (Ni,Co,Fe)based alloys and copper clad aluminum thin wires. The mechanical properties are directly linked to the ratio thickness over grain size (t/d ratio) of the parts.These metallurgical considerations must be taken into account when we are concerned by numerical simulation of the process of such components. It is shown that the simulations can correctly reproduce the softening effect linked to a decrease in thickness and in number of grains across the thickness. Finally the effect of a moderate increase in temperature on these results will be briefly reported. [less ▲]

In this study, samples of stainless steel AISI 316L have been processed by selective laser melting, a layer-by-layer near-net-shape process allowing for an economic production of complex parts. The ... [more ▼]

In this study, samples of stainless steel AISI 316L have been processed by selective laser melting, a layer-by-layer near-net-shape process allowing for an economic production of complex parts. The resulting microstructures have been characterised in details in order to reach a better understanding of the solidification and consolidation processes. The influence of the processing parameters on the mechanical properties was investigated by means of uniaxial tensile testing performed on samples produced with different main orientations with respect to the building direction. A strong anisotropy of the mechanical behaviour was thus interpreted in relation with the microstructures and the processing conditions. [less ▲]

Additive manufacturing processes such as laser cladding (LC) or selective laser melting (SLM) appear very promising in view of an economic near-net-shape production – and also, in the case of LC, the ... [more ▼]

Additive manufacturing processes such as laser cladding (LC) or selective laser melting (SLM) appear very promising in view of an economic near-net-shape production – and also, in the case of LC, the restoration - of complex and (almost) fully dense parts from Ti alloys. Both techniques involve the melting of a metallic powder with a laser. In the SLM process, the metallic powder is deposited layer by layer in a powder bed and then molten locally according to the desired shape, whereas in LC, the metallic powder is directly projected onto a substrate through a nozzle coaxial with the laser beam. The present research aims at comparing Ti-6Al-4V samples processed by these two techniques with reference samples produced by electron beam melting (EBM), another well established additive manufacturing process (patented by Arcam AB Company) in which a powder bed is molten locally by means of an electron beam. In all three processes, the melt pool undergoes an ultrafast cooling and solidifies very rapidly once the beam has left the area, thus giving rise to strongly out-of-equilibrium microstructures. Yet, each one of these processes also has its own specificities e.g. in terms of scanning strategy and of working atmosphere (low vacuum vs. protective Ar flow). In the present work, the microstructures obtained by these three processes have been compared in details, with a particular attention for characteristics such as porosity, grain size, and the various phases present. Since epitaxial growth of the newly deposited layer on the material previously solidified has been shown [1, 2] to exert a strong influence on the microstructure and on the resulting mechanical properties, great care has been taken to study the microstructural anisotropy associated with each one of the three processes. [less ▲]

Mg-Al-Zn alloys have been reinforced with carbon fibres using either the liquid state process of squeeze casting (SC), or friction stir processing (FSP), a solid state process developed more recently and ... [more ▼]

Mg-Al-Zn alloys have been reinforced with carbon fibres using either the liquid state process of squeeze casting (SC), or friction stir processing (FSP), a solid state process developed more recently and that appears as a promising alternative for the large-scale production of C-Mg composites. Both processes have shown their ability to produce sound composites with enhanced strength compared to the non-reinforced alloys. in SC composites, the unsized woven C fabric remains intact while in the FSP composites the sized C fabric is fragmented in short fibres, with an aspect ratio typically equal to 4, homogeneously distributed in the Mg alloy matrix. [less ▲]

In most papers dealing with tension and/or compression tests, the conventional yield stress is determined either by an offset method (usually 0.2% strain) or by back extrapolation from the stress-strain ... [more ▼]

In most papers dealing with tension and/or compression tests, the conventional yield stress is determined either by an offset method (usually 0.2% strain) or by back extrapolation from the stress-strain curve. In our experiments on ECAP‟ed Aluminium a transient hardening saturation (THS) is always observed during the compression tests, but not during the tensile tests. This THS occurs at a significantly lower stress than the conventional yield stress. The aim of the present paper is to determine which the “real” start of yielding is. Two different experimental approaches have been adopted, confirming that the THS stage is exactly the yielding stage. This is not unimportant because it increases the tension-compression asymmetry and hence the back-stress and kinematic hardening. The reason for this different behaviour between tension and compression can be ascribed to a different change in strain path with respect to the ECAP deformation. [less ▲]

In our recent work, a new integrated model was proposed to describe the back-stress evolution based on the dislocation substructure and texture. By relating the back-stress to the dislocation density in ... [more ▼]

In our recent work, a new integrated model was proposed to describe the back-stress evolution based on the dislocation substructure and texture. By relating the back-stress to the dislocation density in cell walls and in the cell interior, this model is able to capture the back-stress evolution of ECAP processed pure aluminium. In this paper, the model is used for another FCC material, namely copper. The aim is to check whether this model is able to predict the tension/compression asymmetry (due to the back-stress) of copper. The results show that this is indeed the case and it is also found that the strain rate ratio proposed in our previous work [1] is a function of the dislocation density ratio. [less ▲]

Phenomenological yield criteria are generally described by many material parameters. A technique to identify these parameters is required to find the best fit to the results of the mechanical tests. The ... [more ▼]

Phenomenological yield criteria are generally described by many material parameters. A technique to identify these parameters is required to find the best fit to the results of the mechanical tests. The parameter identification by the classical simulated annealing technique is presented in this paper. This algorithm, based on Metropolis’ works [1,2], is a global optimization method that distinguishes between different local optima to reach the global optimum. The anisotropic model used in this study is the one proposed by [3]. To prove the efficiency of the proposed algorithm, the material parameters of Ti6Al4V titanium alloy are identified and compared with those obtained using different identification procedures and the same experimental data. [less ▲]

This paper is concerned with the numerical simulation of hot metal forming, especially superplastic forming. A complete thermo-viscoplastic formulation at finite strains is derived and a unified stress ... [more ▼]

This paper is concerned with the numerical simulation of hot metal forming, especially superplastic forming. A complete thermo-viscoplastic formulation at finite strains is derived and a unified stress update algorithms for thermo-elastoplastic and thermo-elastoviscoplastic constitutive equations is obtained. The resulting unified implicit algorithm is both efficient and very inexpensive. Finally, numerical simulations of superplastic forming are exposed. [less ▲]